1. Field of the Invention
The present invention relates to semiconductor devices and, more particularly, to a semiconductor device for reducing effects of noise on a circuit in a semiconductor device.
2. Description of the Background Art
A conventional semiconductor device for reducing effects of noise upon an internal circuit is disclosed in, for example, Japanese Patent Laying-Open No. 5-128855.
FIG. 28 is a schematic block diagram showing a conventional semiconductor device.
Referring to FIG. 28, a conventional semiconductor device 5 includes a package frame 1, a bonding wire 3, a pad 11, an internal power supply line 1511, an internal circuit 21, a stabilize circuit 23 which is to be stabilized, a GND package frame 7, a GND bonding wire 9, a GND pad 17, and an internal GND line 19.
Bonding wire 3 has one end connected to package frame 1 and the other end connected to pad 11, which is also connected to internal power supply line 1511. Internal power supply line 1511 is connected to internal circuit 21 and stabilize circuit 23. GND bonding wire 9 has one end connected to GND package frame 7 and the other end connected to GND pad 17, which is also connected to internal GND line 19. Internal GND line is connected to internal circuit 21 and stabilize circuit 23.
Internal circuit 21 and stabilize circuit 23 of semiconductor device 5 receive an externally applied power supply potential through package frame 1, bonding wire 3, pad 11 and internal power supply line 1511. Internal circuit 21 and stabilize circuit 23 of semiconductor device 5 also receive an externally applied power supply potential (such as a ground potential) through GND package frame 7, GND bonding wire 9, GND pad 17 and internal GND line 19, which potential is different from the power supply potential applied through package frame 1.
Internal circuit 21 is provided in semiconductor device 5 and associated with the operations thereof. In other words, it is a circuit which brings about noise, including a word line drive circuit, a data bus drive circuit, and a data output circuit.
Stabilize circuit 23 is easily affected by noise, such as a circuit for controlling a signal of a small analog value and a circuit operating with an extremely small current (for example, on the order of .mu.A) when semiconductor device 5 is in a standby state. The circuit for controlling a small analog value includes a reference potential generation circuit.
Internal circuit 21 consumes a considerable amount of electric power during operation. As a result, noise is generated at internal power supply line 1511 and internal GND line 19.
FIG. 29 shows the noise level generated when internal circuit 21 of semiconductor device 5 operates.
As indicated by an arrow a, noise of a level lower than that of a power supply potential Vcc is generated at internal power supply line 1511. As indicated by an arrow b, noise of a level higher than a ground potential GND level is generated at internal GND Line 19.
Although such noise is somewhat absorbed by a lowpass filter including an interconnection resistance and a parasitic capacitance of internal power supply line 1511 and a lowpass filter including an interconnection resistance and a parasitic capacitance of internal GND line 19 during propagation to stabilize circuit 23, significant effects are given to stabilize circuit 23.
As described above, a power supply line for applying power supply potential Vcc is common to internal circuit 21 and stabilize circuit 23 in the conventional semiconductor device 5. In other words, power supply potential Vcc is applied to internal circuit 21 and stabilize circuit 23 through internal power supply line 1511. Consequently, noise accompanied with operation of internal circuit 21 is provided to stabilize circuit 23 along with power supply potential Vcc. Therefore, malfunction is undesirably caused at stabilize circuit 23.
Ground potential GND is provided to internal circuit 21 and stabilize circuit 23 through internal GND line 19. Therefore, noise accompanied with operation of internal circuit 21 is also provided to stabilize circuit 23 along with ground potential GND, thereby causing malfunction of stabilize circuit 23.